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Full text of "The Cambridge Natural History"

CARPUS  AND TARSUS   OF ARTIODACTVLES

271

the facts  of Ungulate  descent are absolutely destructive of any
such comparisons.

As is the case with the Perissodactyles, the Artiodactyles
show a historical series, the primitive five-toed condition being
almost preserved in Oreodon, up to the most modern modification
exemplified by the Ox, Sheep, etc., in which animals there are not
even vestiges of the fourth and fifth toes. It has been stated,
however, that the foetal Sheep has traces of
those rudiments. The so-called cannon bone
(the fused third and fourth nietapodia) is
accompanied in its fusion by an increase in
length. At the same time the functional
middle metacarpals push aside the rudiments
and, forming a broad surface for that purpose,
articulate with the magnum and uneiforni
bones to the exclusion of the rudiments.
This lias been termed an " adaptive reduc-
tion/* In the " inadaptive reduction " there
is the same reduction of the metacarpals,
but the rudiments still articulate as in the
primitive Artiodactyle foot, i.e. Me II with
trapezium, trapezoid, and magnum ; Me III
with magnum and unciform ; Me IV and "V
with unciform. This would appear to give FlGi 1S9. Doriianrfaceof
greater solidity and consequently greater rfgb-t tarsus of Bed Deer

x            4.V,   4.     4.^     *     4.                                                                        (O&rmts elapAu*).

Strength to the foot.

The   carpal "bones   of  the   Artiodactyla

, ,                                          ,        .        >*     .                                        , .      -.    . .                                             , ,                                             -      -

alternate in then: articulation; the primi-
tive state of affairs1 is not retained even
in the earliest types. The femur has no
third trochanter, so prevalent in the Perissodactyles. In the
hind-foot the calcaneum has an articular facet for the fibula,
which is not characteristic of the Perissodaetyla. In the more
modern forms, e.g. the Cervidae, the navicular and cuboid loecome
f used into one bone ; and there are even further fusions whioh
will be referred to later as characteristic features of different
groups. It is interesting to notice that the reduction begins
earlier and is clearer in the hind-foot than in the fore. One

Astragalus ;    e,  cal-

caneum ; c8, cuneiform ;

<%* cuboid ; mJ/J, ml K,

metatarsais; a, na.vicu-
(F*m   Blower's

1 See,  liowever,  p.   196,   for a discussion  as   to   wliiclb, is tlie more  primitive
arrangement,